Modern automatic transmissions generally include several overrunning roller clutches. The roller clutches are each installed between a cam race and a pathway race, and each race is in turn joined to one part of a selective torque transfer mechanism. The interposition of the roller clutch between the two parts of the torque transfer mechanism acts to improve the timing and quality of shift as the gears change ratio. In modern roller clutches, known as concentricity control clutches, the clutch cage also includes a series of bearing surfaces that ride on a cylindrical surface of the pathway race, known as the the pathway, thereby keeping the races basically coaxial to one another. The cage is typically molded of nylon or some other suitable material, and may be molded in one piece. The cage is installed to the cam race before the pathway race is added, and does not move or turn relative to the cam race as the clutch operates. However, the pathway rides over the cage bearing surfaces very rapidly as the clutch overruns, and it is desirable, especially in high speed clutches, to provide a film of lubricant between the pathway and the cage bearing surfaces to reduce friction and wear.
A known means of supplying lubricant to the pathway-cage bearing surface interface may be seen in the first three Figures of the drawings, in which:
FIG. 1 is a sectional view of a mounting drum of a transmission, clutch races and clutch taken along the line 1--1 of FIG. 3;
FIG. 2 is an enlargement of a portion of FIG. 1;
FIG. 3 is a sectional view taken along the line 3--3 of FIG. 1.
Referring to FIGS. 1 and 3, a conventional roller clutch cage is indicated generally at 10, which has several typical features. Cage 10 is integrally molded of nylon or other suitably tough plastic with a spaced series of partially cylindrical bearing surfaces 12 on its outer periphery. Between adjacent surfaces 12, a like number of open roller pockets 14 each contains a spring energized roller 16. The innermost edge on the inner face of cage 10 is rounded at 17, for a purpose described below. Cage 10 fits closely between an inner cam race, indicated generally at 18, and an outer pathway race, indicated generally at 20. Cam race 18 has the usual series of spaced cam ramps 22, and cage 10 is fixed to the cam race 18 by fitting it onto the cam ramps 22 by the usual push and twist method. After installation, therefore, cage 10 does not turn relative to cam race 18. The cam race 18 forms an annular space with a cylindrical surface, or pathway, 24 of pathway race 20. As the races 18 and 20 overrun, pathway 24 is maintained coaxial to cam race 18 by riding over the cage bearing surfaces 12. Cam race 18 also has other features intended to cooperate with other structure that is part of the automatic transmission environment, which is described first.
Still referring to FIGS. 1 through 3, a mounting structure, in this case a drum indicated generally at 26, has the form of a stepped cylinder with a generally L shaped cross section. Drum 26 has a larger diameter sleeve 28, a coaxial smaller diameter sleeve 30, and a flat face 32 that is perpendicular to the axis of drum 26. Several oil holes 34 drilled through the smaller sleeve 30 open right at the intersection of smaller sleeve 30 and face 32. Drum 26 is part of a selective torque transfer mechanism within the transmission, which would also include a stack of piston activated friction disks splined to the inside of smaller sleeve 30, a similar stack splined to the outside of pathway race 20, and a band applied to the outside of sleeve 30, none of which need be illustrated to explain the invention. As the drum 26 and pathway race 20 are selectively powered or held, the roller clutch serves the speed matching, shift smoothing function described above. It should be understood that, in the specific environment involved here, the drum 26 will have a significant absolute speed during clutch overrun, and the pathway race 20 may, as well.
Still referring to FIGS. 1 and 3, the inner face of cam race 18 has a chamfer 36 along its entire inner edge, and a plurality of spaced radial grooves 38 cut across the inner face and into chamfer 36. Chamfer 36 and groves 38 coact with drum face 32 after the cam race 18 has been secured to drum 26 as follows. First, cam race 18 is secured to drum 26 by pushing it tightly over the outer surface of smaller sleeve 30, until the inner face of cam race 18 abuts with the mounting drum face 32. The oil holes 34 are assured of opening into chamfer 36, since chamfer 36 covers 360 degrees. The closed passage formed between the chamfer 36, grooves 38 and the drum face 32, together with the oil holes 34 that open into chamfer 36, comprise a closed and pressurized oil path that ends at the radially outer edge of cam race 18. Then, cage 10 is fitted onto the cam ramps 22 as described above. Next, the pathway race 20 is pushed in over rollers 16 and twisted into place. Finally, a snap ring 40 is fixed to the drum's smaller sleeve 30. Snap ring 40 serves only to prevent cage 10 and pathway race 20 from moving too far away from drum face 32, since cam race 18 is held to smaller sleeve 30 completely by a friction fit. Cage 10 and pathway race 20 are not tightly confined between snap ring 40 and drum face, as is indicated by the clearance shown between the inner faces of cage 10, pathway race 20, and drum face 32.
Referring next to FIG. 2, during the operation of the transmission, lubricating oil is continually pumped under pressure through the oil holes 34 by a transmission pump that is not illustrated. Oil leaves the oil holes 34, still under pressure, and enters the area between the chamfer 36 and drum race 32. Oil can flow in either direction as it enters the area between chamfer 36 and drum face 32, but the arrows indicate only the flow clockwise, for simplicity. Next, pressurized oil enters the area between the grooves 38 and the drum face 32, flowing radially out. The oil remains under pressure only until it leaves the radial grooves 38 at the radially outer edge of cam race 18, which is where the closed path described above ends. At that point, the oil loses pressurization, and the centrifugal force of the rapidly counterclockwise rotating drum 26 will then throw much of the oil radially out through the clearance between the inner face of cage 10 and the drum face 32. The oil that escapes is effectively lost for purposes of lubricating the cage bearing surfaces 12, and its flow path is not indicated by arrows. At least some of the oil, however, will splash out in both directions along the channel formed between the cage rounded edge 17 and the drum face 32. Again, for simplicity, only the clockwise flow in that channel is shown. Some of that oil will eventually reach the open pockets 14. The pockets 14 represent an available path for oil to be thrown radially outwardly and into the pathway 24. Although pathway 24 may or may not be rotating rapidly in the absolute sense during clutch overrun, it will be rotating rapidly relative to the oil that comes into contact with it through the pockets 14. That oil is then sheared or pulled into the interface between the adjacent bearing surface 12 and the pathway 24, its target area. As the arrows indicate, oil flow to the target area is far from direct. Given the convoluted path, the fact that the oil loses pressure when it leaves the grooves 38, as well as the leakage losses, a great deal of oil must be provided through the oil holes 34 to make sure that enough reaches the target area. This can be costly in terms of pump capacity. Moreover, a given pump capacity may be inadequate if it is desired to increase the relative speed between the bearing surfaces 12 and the pathway 24 during overrun. This conventional type of lubrication is generally referred to as splash lubrication, because the pressure is lost once the oil reaches cage 10.